In a cross-sectional study, 5-, 7-, and 9-year-old-children and adults (N = 144, 86 females, predominantly White U.K. sample of lower-middle to middle-class background) were interviewed about their experiences of involuntary autobiographical memories (IAMs) and semantic mind-pops that come to mind unintentionally. Although some age differences emerged, the majority of participants in all age groups claimed familiarity with involuntary memories and provided examples from their own experience. Moreover, the self-reported frequency of IAMs and mind-pops was high, and reported IAMs usually referred to incidental environmental triggers, whereas reported mind-pops did not. This age invariance highlights the ubiquity of involuntary memories across development and opens up interesting avenues for developmental research on involuntary memories and other spontaneous phenomena (e.g., mind-wandering, future thinking).